Seminar report on " OPTICAL ETHERNET "LAN forms basis of all commercial,research,and data communication networks.Recently an increase in applications demand significantly higher bandwidth. Ethernet is an easy to understand and extremely cost-effective technology.For these reasons, 98% of local area network (LAN) connections are nowEthernet based. To meet this,high speed LAN types have been developed ,includinga number of variations of basic ethernet LANs. CSMA/CD(carrier sense multipleaccess with collision detection) is used widely in wired LANs as a MAC(MediumAcess Control) method. Transmission medium is coaxial cable (ether) up to2.5km long,with repeaters at every 500meters.Upto 256 machines could beattached to the system via transceivers screwed onto the cable.The system ran at2.94Mbps Definition Optical Ethernet is the technology that extends Ethernet beyondthe local-area network (LAN) and into metropolitan-area networks (MANs) andwide-area networks (WANs). While Ethernet LANs are almost exclusively usedwithin the enterprise, optical Ethernet technology can be used as a serviceprovider offering. Key components of Optical Ethernet are the abilities tosegregate traffic of different users and to deliver the particular service level eachuser purchases They combine the flexibility, simplicity and cost effectiveness ofEthernet with the reliability, speed and reach of optics to allow users to extendtheir LAN environment across the MAN and WAN.
Overview Optical repeaters were part of the first Ethernet standard back inthe early 1980s. Today, optical Ethernet advances promise to take Ethernettransport to levels undreamed of back then and not even feasible using coppertechnologies today. Thanks to advances in optical Ethernet, this most common(and most standard) of LAN technologies will soon be the most common (andmost standard) of WAN technologies. The history and potential of optical Ethernettechnology is explained , focusing specifically on its impact on service-providernetworks and services. Technology Ethernet was defined as an open standard in the early 1980s bya consortium comprised of Digital Equipment Corp., Intel, and XEROX; theresulting standard was called the DIX Ethernet Spec. The goal was to promote arelatively high- performance and low-cost LAN implementation using digital(baseband) signaling on a shared coaxial cable. In 1983, the IEEE 802 Local-Area Network/ Metropolitan -Area Network Standards Committee (LMSC) released the 802.3 standard forEthernet—a shared medium for LANs using a distributed media access control(MAC) mechanism called carrier sense multiple access with collisiondetection(CSMA/CD). Ethernet has proven to be a highly flexible standard. It has evolved toinclude point-to-point signaling, full-duplex (unshared) links, and very-high-speed networks. Several Ethernet characteristics have persisted, the mostimportant of these being the framing format itself . An Ethernet frame specifies a minimum and maximumpacket size, a “protocol-type” field (expanded by 802.3 to function sometimes as apacket-length field), and both a destination and a source MAC address. The
address fields have been particularly valuable, as the globally unique MACaddresses (each 48 bits long) have enabled the creation of new devices (Ethernetswitches) that have simplified the development of large Ethernet networks. Optical links have been a part of Ethernet standardssince the early 1980s. The needs and potential of optical transport, includingpoint-to-point and full-duplex links, have driven some of the evolution ofEthernet. Optical Ethernet technologies are providing the longest spans andgreatest speeds used in LANs today, and they will undoubtedly, continue to do soin the future. The figure shown below reveals the frame format of ethernet .HistoryThe First Optical Ethernet Repeaters The first Ethernet standard included a provision for a single 2-km optical repeater in an Ethernet LAN that was expected to be used to linkdifferent buildings in a large LAN. As parts of a shared LAN, these links were notonly half- duplex—they also propagated collisions (the signals used to limit accessto a single sender at a time). Their spans were limited by the maximum delay thatcould be allowed on an Ethernet LAN and still detect collisions. They were trueLayer-1 repeaters.Campus Optical Ethernet The advent of the Ethernet “bridge,” now commonly called anEthernet “switch,” changed the game. The purpose of an Ethernet bridge is toconnect two different Ethernet LANs (the name “switch” evolved to denoteinterconnecting more than two). This occurs at the MAC layer, Layer 2 of the 7-layer OSI protocol model, and there are two important features involved. First,not all traffic on either end is transported — only traffic destined for the “other”LAN. Second, collisions (and collision-detection signals) are not transported; each
side is its own Layer-1 LAN. Together, these features not only improve networkperformance by isolating LAN segments but also greatly increase the maximumsize of an Ethernet LAN. The Ethernet bridge enabled large LANs to be deployed because anetwork of campus “bridges” could interconnect all of the building LANs. Insteadof forming a simple “star” network, these were implemented as meshes, withmultiple connections to each LAN. This required the development of thespanning-tree protocol (802.1D), which works by disabling redundant paths andwhich implements a form of path protection for the LAN. People quickly realized that if both ends of an optical linkterminated on a bridge port, then the normal limits on the size of an Ethernet LANsegment no longer applied. The optical link could be operated as full-duplex,thereby doubling the bandwidth of the link. And with only one transmitter on aLAN segment, there could be no collisions; thus, the need to limit the size of thespan for collision detection vanished, allowing an optical Ethernet segment tospan as far as the lasers could reach. In the early days, this still meant only a few kilometersbecause light emitting diodes and multimode fibers were used; but this was stillenough to enable large campuses to be fully connected. The loss of collisions as aflow-control mechanism required the development of a new protocol, 802.3x, tohandle that need.Optical Fast Ethernet In 1995, a new standard emerged for 100–megabits-per-second (Mbps) Ethernet transmission (or “Fast Ethernet”) over Category-5 (Cat-5) unshielded twisted pair (UTP) copper cable. Actually, several standards wereproposed and implemented, but only one gained significant acceptance—that was100BASE–TX using two Cat-5 UTPs at distances up to 100 meters.
Following close on the heels of the “copper” Fast Ethernetstandards development was the optical side. The first standards to emerge wereadapted from fiber distributed data interface (FDDI) technology. The transceiverdesign and encoding technique were the same, simplifying the work of thestandards committee and ensuring that the standardized technology wouldactually work. While there were some differences, considerable effort wasexpended to make sure that FDDI transceivers could be readily adapted to opticalFast Ethernet. As on the copper side, several standards were ratified on theoptical side. The first standard was for medium-range multimode fibertransmission at 1310 nm (100BASE–FX), based upon the FDDI standards. Thisprovided for a normal range of about 2 km—adequate for most campusenvironments. 100BASE–FX was part of the original 802.3u Fast Ethernetspecification back in 1994. The second optical fast-Ethernet standard was100BASE-SX, ratified in June of 2000 (a full six years later). This standard enabled backward compatibility with 10BASE–FL by using thesame 850 nm wavelength and an auto-negotiation protocol. There was no single-mode fiber standard for optical Fast Ethernettransmission (and there is still none at the time of this writing, nor is oneexpected). This lack of a formal standard has not stopped equipmentmanufacturers from implementing longhaul (10 km – 100 km) fast-Ethernetlinks, and in practice they are likely to be interoperable, at least when operating atthe same wavelength. They are available both at 1310 nm (the wavelength used in100BASE-FX, FDDI, and SONET equipment) and 1550 nm (the wavelength usedin wavelength division multiplexing [WDM] systems). This de facto compatibilityhas resulted from the evolution of Ethernet devices, which originally separated thedigital logic from the analog logic.
This distinction was formalized in the Fast Ethernet standardas the media independent interface (MII). Today, the chip sets that handleEthernet are generally independent of the chips that handle the media, be theycopper, fiber, or potentially something else. Moreover, the fiber-optic driversthemselves don’t know (or care) if the fiber is multimode or single-mode, what thetype of connector is, or what wavelength is being used. The bottom line is that theapproach used by Ethernet component manufacturers has led to a great deal offlexibility and interoperability, often transcending the standards that werecreated for that very purpose.Optical Gigabit Ethernet The 802.3z gigabit Ethernet standard describes multiple opticalspecification. 1000BASE–SX describes short wavelength (850 nm) transmissionusing multimode fiber with a maximum range of 550 meters on new fiber, or 220meters on older fiber (with poorer dispersion characteristics). 1000BASE–LXdescribes long-wavelength (1310 nm) transmission using either multimode fiber(with a range of 550 meters) or single-mode fiber (with a range of 5000 meters).As before, the standards committee took full advantage of existing technology and“borrowed” the transceivers and encoding formats of fiber channel. Specifically,the FC–0 fiber driver/receiver was copied, along with the FC–1 serializer/deserializer. The 8B/10B encoding format was used, which specifies the framingand clock-recovery mechanism. The significant changes were the signaling rate,which was increased to 1.25 gigabits per second (Gbps) from fiber channel’s 1.06Gbps, and the frame content and size, which are the same as previous Ethernetimplementations. Much of the early gigabit Ethernet standards work was in specifyinghalf-duplex operation in a collision detection environment equivalent to theshared LANs of ordinary and Fast Ethernet. However, that work was effectivelywasted—all commercial Gigabit Ethernet implementations today are point-to-
point, full- duplex links. Just as in Fast Ethernet, the range of commercially available opticalGigabit Ethernet interfaces exceeds the limits outlined by IEEE 802.3z. There aredevices available that operate at 1550 nm and devices that operate at muchgreater distances than 5km. In fact, 150km spans are possible without repeaters oramplifiers. Again, this was enabled by the separation of Ethernet control logicfrom media control logic, which has now been formalized in a new way. It is notthe formal definition of an MII (called gigabit MII [GMII] in the Gigabit Ethernetstandards), but rather a new standard for a GigaBit Interface Converter (GBIC).GBIC modules Originally specified for fiber channel, the GBIC standards have evolvedto support Gigabit Ethernet, and these modules have become the de factostandard for gigabit Ethernet interfaces. They provide hot-swappable modulesthat can be installed to support LAN, campus area network (CAN), MAN, and evenWAN transport interchangeably, as needed. And they are available from a largenumber of suppliers, keeping prices competitive and capabilities expanding. The GBIC revolution is one of the best examples of industry consortiacreating a new market by consensus, yielding a net increase in the revenues of allthe participants. The modules themselves, by virtue of being small and plugginginto a standardized slot, challenged the transceiver manufacturers, whoresponded with technological innovations and features beyond all reasonableexpectations. The chip manufacturers contributed readily available chip sets thatsupport these GBIC modules, simplifying and speeding up the task of thehardware engineers.Optical Ethernet Today
Optical Ethernet systems are evolving beyond mere “optical links”that interconnect isolated LANs. Rather, they are becoming systems inthemselves, providing scale and functionality that is simply not feasible withcopper-based Ethernet, including those linked by routers.LAN Today, few optical Ethernet links are implemented within acomputer room or small building. But there are exceptions for electrically noisyenvironments, highly secure transmissions , and ground isolation. And even in asmall building, it is easier to run fiber-optic conduit than electrical wires becausethere are fewer issues with building codes. Traffic segregation is accomplished byusing the IEEE 802.1pQ virtual LAN (VLAN) standard. This standard lets OpticalEthernet networks mark each users traffic with a VLAN tag as it enters thenetwork and then use this tag to keep each users traffic separate as it crosses thenetwork. Of course, 802.1pQ was designed for enterprise networks and thenumber of possible VLAN tags is too low. Work is under way in IEEE to extendthis number from 4,096 to approximately 16 million. This situation is likely to change, as very-short-reach opticssupport much higher speeds than copper does. It is important to note that gigabitcopper links are limited to about 30 meters and that the next generation ofEthernet at 10 Gigabits would drop this already inadequate distance dramatically.CAN Today, virtually all Ethernet links greater than 200 meters areimplemented optically. The CAN is dominated by multimode fiber, although mostCANs are really multiple LANs interconnected by routers that use optical links.This situation is changing, as the scale and functional capabilities of Ethernetswitches increase. Ethernet 10BASE–T hubs, once dominant, no longer offer a sufficientlylower cost to justify their use. More and more LANs are being implemented with
Ethernet switches, providing separate switch ports to every node on the LAN. Traditionally, these Ethernet switches aggregate traffic into a high-speed uplink port (once Ethernet, then Fast Ethernet, and now Gigabit Ethernet),which feeds a router that itself interconnects the LANs and provides WAN access.But today, when the cost of a router is weighed against the cost of a GBIC module,it loses every time. This trend is being accelerated by the proliferation of virtual LAN(VLAN)–capable Ethernet switches and by the development of even larger andmore capable routers that understand and route to VLAN IDs in the now largerLAN.MAN Optical Ethernet in the MAN is a relatively recent development.Gigabit optical Ethernet has the capacity to provide direct Ethernet services as acarrier offering, with service switches that limit actual delivered bandwidth asneeded. Multiple vendors now offer direct Ethernet services to subscribers, withonly a few core routers linking those subscribers to the outside world (theInternet). But “Ethernet services” is not the leading reason to implement anEthernet MAN today. Rather, the desire to reduce the number of routers in thenetwork is becoming the most compelling reason to use a Layer-2 technology(Ethernet) in the metro area. The reason is simple—every router in a path, manyof which are unnecessary, adds delay to thepacket transport. In an ideal world, routers provide a buffer betweenmanagement domains, which are generally companies or network providers. They provide a place to control access, provide security (viafirewalls) and manage addresses. But within a management domain, layers of
routers generate excess complexity and require large staffs of “router guys.” Theyalso bypass a primary tenet of many routing protocols—that every router shouldhave a direct link to every other router that it knows about.Based fundamentally on Ethernet, Optical Ethernet MANs let carriers deliverstandard, well-known 10/100M bit/sec or 1G bit/sec Ethernet interfaces - thesame as those used to easily connect office networks today. Instead of a SONET ring, the metropolitan backbone for OpticalEthernet networks will be based on the 10G bit/sec Ethernet standard from theIEEE working group 802.3ae. Optical technologies enable Ethernet networks to extend over muchgreater distances than campus Ethernet nets. Running over single-mode fiber,Optical Ethernet lets links in the network range from 3 to more than 6 miles inthe case of 1310-nm wavelength technology, and up to 43.4 miles for 1550-nmwavelength technology.WAN Ethernet transport has not yet taken off in the long-haul network, butthis is expected to change as 10-Gigabit Ethernet interfaces become available.Some of those are expected to operate at SONET OC–192 speeds and at thedistances needed for long-haul networks. The distance limitations are not aserious concern because most long-haul networks use densewavelength division multiplexing (DWDM) systems to combine multiple circuitsover a single fiber, each on its own wavelength, and these DWDM systems providethe long-haul capability themselves. Still, wide-area Ethernet networks areexpected to be implemented, the main reasons being speed, cost, andsimplicity. Consider a nationwide 10-gigabit IP SONET–style ring implementedas OC–192 packet-over–SONET (POS) links between a dozen cities. Each citywould need a large router with two relatively expensive POS ports, and theaverage packet would traverse half a dozen routers as it crossed the network. Inthe event of a link failure, the routers would spend a significant span of time
converging on a new set of routing tables to bypass the failure. Now consider the same network with each city containing anEthernet switch with two 10–Gigabit Ethernet switch ports and a 1-gigabit portconnected to the local router. Total costs here would be much lower because 10–Gigabit Ethernet switch ports are expected to be much less expensive than theequivalent router ports, and 1-gigabit router ports are relatively inexpensive. Today, several vendors have products that aggregate and transport Ethernettraffic at 10-gigabit speeds suitable for the WAN. These are proprietary, requiringmatching devices from the same vendor at each end— normally not a problem in afull-duplex, point-to-pointnetwork.Featured Products & Solutions:Ethernet over Fiber Ethernet over Fiber is primarily deployed in a point-to-point or meshnetwork topology, and delivers packet services over dark fiber typically in theMetro Area Network (MAN).Ethernet over RPR Ethernet over RPR solution is through next-generation SONETproducts that enable simplification of network provisioning, elimination ofSONET bandwidth waste, improvement of bandwidth efficiency, and link-layerprotection.Ethernet over SONET/SDH Ethernet over SONET/SDH solutions deliver high-QoS EthernetPrivate Line services across an arbitrary multi-domain SONET/SDH network,addressing established service providers who want to develop maximum returnon network infrastructure assets.Ethernet over WDM
Ethernet over Coarse/Dense Wave Division Multiplexing (WDM) isparticularly effective in high-bandwidth, extreme-performance scenariosRecent TrendsOptical Ethernet Switches A true “all-optical network” is not likely to happen in theEthernet space in the foreseeable future. The reason for this is that there are notechnologies that enable packet switching at the optical layer today. However,purely optical Ethernet switches have already been demonstrated, in the sensethat all of the Ethernet interface ports are optical (while the internal switchingremains electrical). This is today’s technology optimized for carriers selling Ethernetservices. When a carrier’s customers are spread over metropolitan distances (10km – 50 km), then the lowest-cost service-provider network is Ethernet with all ofthe device ports themselves being optical. Businesses are requesting native Ethernet services to interconnecttheir facilities into VLANs. This trend will be accelerated by the fiber-to-the-consumer move, as the lowest-cost optical service will once again be Ethernet. Sothe bulk of early fiber-to-the-home (FTTH), and possibly the majority of fiber-to-the-business (FTTB) services, may well be optical Ethernet (at least as viewed bythe carrier).GBIC Modules The latest GBIC innovation is a mini–GBIC, also known as the smallform-factor pluggable multisource agreement (SFP MSA) module. The mini–GBIC is only about half the size, effectively doubling the available capacity thatcan be designed into the face of an equipment shelf. New designs are quicklytaking advantage of this space savings.
Resilient Packet Rings (RPR) While not formally a part of Ethernet, the IEEE 802.17 committee iscreating a standard for packet transport over fiber-optic rings. Current directionsinclude using Ethernet framing in SONET–style rings. The goal of RPR is simple:to define a high-performance, high-availability optical transport suitable forcarrier networks in metropolitan service areas. Note that it is easier to implementa fast and robust link-failure recovery in a ring topology than in a mesh topology;this is because in a ring, the alternate route is always known. The IEEE 802.17 committee does not view RPR as Ethernet, andindeed there is no intent that an IEEE 802.3 device could be directly connected toan 802.17 interface. To a degree, a metro Ethernet is a competing mesh (not ring)technology with relatively slow spanning-tree failover, instead of SONET–style,fast (50 ms) failure recovery. Still, RPR implementations are likely to become apopular transport mechanism for Ethernet packets, especially fortelecommunications service providers
10-Gigabit Ethernet Proposed Standards The 10GEA (10-Gigabit Ethernet Alliance) is an industryconsortium of about 100 members working to promote the acceptance andsuccess of 10-gigabit Ethernet. This group is not the same as the IEEE 802.3aestandards committee, which is working on a set of proposed standards for 10-Gigabit Ethernet. The manufacturers are not passively waiting on a standard, asmultiple vendors expect to announce 10-Gigabit Ethernet products during 2001,in advance of the standards ratification expected in March 2002. Of course, eachof these vendors hope that their products will be one of the standards, and theypromise that they will conform once those standard interfaces are defined.10-Gigabit Ethernet May Be Optical Only here are real challenges to making electrical signals carry asignificant distance at those rates, and the implementations may simply be moreexpensive than their more capable optical cousins (meaning that they simplywon’t happen). One of the proposed standards uses very-short-reach optics, to beimplemented as parallel data streams over a fiber-optic ribbon containing 12multimode fibers. This was proposed as a low-cost method to interconnect devicesin a room. A second proposed standard uses a very compact package (about 1" x0.75" x 3") containing a coarse WDM device, four receivers, and four lasersoperating approximately 25 nm apart in wavelengths near 1300 nm. Eachtransmitter/receiver pair operates at 3.125 gigabaud (data stream at 2.5 Gbps).The proposed device has very aggressive engineering challenges and a veryaggressive target-price point.
A third proposed standard is a serial interface using 64B/66Bencoding (instead of the 8B/10B used in gigabit Ethernet), a data stream of10.000 Gbps, and a resulting clock rate of 10.3 Gbps. This is a favorite of theEthernet “purists,” who like the simplicity of just moving the decimal place;moreover, the resulting optical data stream may be directly interoperable withsome of today’s DWDM systems. A fourth proposed standard is a SONET OC–192 compatiblestream, which is therefore clocked at 9.953 Gbps. The disadvantage is that it is nota pure 10 times 100 megabit Ethernet. There may also be disadvantages of cost—SONET is not the least expensive transport method. The advantages, however, arethat it would be guaranteed to interoperate with all of the OC–192 SONETdevices, including the networks of all of the major telephone companies, and all ofthe OC–192 compatible DWDM systems. And the reality is that 9.953 Gbps isclose enough to 10.000 that no “real” applications are likely to notice thedifference.Future Expectations Ethernet is (by a huge margin) the most successful networkingtechnology ever. After all, 99 percent of all TCP/IP packets (including Internettraffic) traverse an Ethernet somewhere (and more likely five or six EthernetLANs in the World Wide Web). And the future is even brighter! The RadianceOptical Ethernet System is a new breed of optical access and connectivity thatprovides a secure, yet manageable, Ethernet demarcation point between theservice provider and business userOptical Ethernet to the Consumer FTTB is a reality for the Fortune 500 today and will be a reality for 95percent of non–small office/home office (SOHO) businesses within just a fewyears. A carrier that runs fiber to a business enables the delivery of all of today’s
communications services and, likely, all of tomorrow’s. And Ethernet services arethe least expensive services that can be provided over that fiber today. FTTH is already in trial deployments in several communities. Severalstudies have been completed suggesting that building an FTTH network is nomore expensive than a full-scale DSL buildout or a two-way cable television(CATV) upgrade, costing in the neighborhood of $1,000 per home passed. Thepotential capacity of an FTTH network is orders of magnitude greater than DSL orCATV, so it is clear that for any new buildout, laying fiber is the logical choice.And just as in FTTB, Ethernet is the least expensive technology providing optical-network access today. It seems clear that Ethernet services will be coming soon tobusinesses near you— and to residences soon after. The only questions are howsoon, how fast, and how expensive? In many metropolitan areas, some serviceproviders already provide Ethernet services by the megabit of capacity: you canbuy from 1 to 100 megabits, as needed A few service providers already sell Fast Ethernet (100 megabit)Internet access for $1,000 per month—a truly compelling price whencompared to the Old World SONET– or ATM–based services. Still, is Fast Ethernet fast enough? Of course, that depends upon thebusiness, but the cost of laying FTTB dominates the capital expenditures, andtoday’s Fast Ethernet infrastructure can be readily upgraded tomorrow. Theswitching cost and Internet-access cost are still much higher for Gigabit speeds,but those costs are rapidly declining. For Ethernet services between locations for abusiness. Gigabit Ethernet may already be needed to support file servers,backup servers, and other intranet applications. After all, most workstations
installed today come with fast Ethernet built-in, implying that the switching andoffice-services infrastructure should be significantly faster to avoid bottlenecking. Residential applications are more limited. 10-Megabit Ethernetshould be adequate for Web browsing for the near future, and the bandwidthneeded for telephony is negligible. The most bandwidth-hungry applicationrecognized today is TV, especially premium services such as video-on-demand. A single channel or movie at broadcast quality requires about 4 Mbps;DVD quality requires only about 9 or 10 Mbps; and even HDTV will probably onlyrequire 20 Mbps. Of course, these figures are per-channel-viewed, and theindustry should plan on an average capacity of perhaps two channels perhousehold at a time. Still, even the most aggressive of these numbers imply that asingle Fast Ethernet service to each home (not shared) is more than adequate forthe services we know of today.Optical Ethernet Area Networks Large optical Ethernet networks are changing the definition of theLAN. “Local” might even be “global.” The original barriers in an Ethernet LAN (3-km span, 1023 nodes, 1 optical repeater) have long since been vanquished. Today,the practical limits are more because of the need to terminate broadcast traffic orto provide security between management domains, or because of today’s limits tothe number of MAC addresses that an Ethernet switch might support. VLANs already start to address these issues; and larger VLAN–enabled switches in the future are at least likely to control the problems andisolate them for a really large router to handle. The practical limits to the size of an optical Ethernet are notgeographic; rather, they involve bandwidth, node count, and overlying protocol(broadcast traffic, routing-table size, etc.). As VLAN and other Ethernet services
become more common, we may even see large corporate networks simplify into asingle, optically connected Ethernet LAN, with only a few large routers providingthe necessary functions of security, address management, and interdomainrouting. The largest optical Ethernet networks are likely to belong tocarriers, interconnecting all of their points of presence (POPs). Even today’soptical Ethernet technology could be used to create a nationwide (or even global),very- high-speed optical Ethernet that can be used to interconnect the large corerouters in each POP. Such a network would have fewer router hops, faster link-failure recovery, and lower cost than today’s “normal” network of OC–192 POSrouters.Beyond 10 Gigabits Just as the growth of 10-Megabit Ethernet led to the need for 100-Megabit Fast Ethernet, and just as the growth of Fast Ethernet led to the need forGigabit Ethernet, the growth of Gigabit Ethernet is now driving the market to 10-Gigabit Ethernet. This trend is not likely to stop anytime soon. Servers—whetherWeb servers, file servers, e-commerce servers, or others—must have greaterbandwidth than the customers they serve, otherwise, those customers will feelfrustrated with inadequate performance and possibly go elsewhere for service.The best example is Web servers. If the average Web browser is using a 56k modem, a server on aT1 line can simultaneously handle approximately 30 customers. But thebroadband movement has already started, and millions of consumers are nowaccessing the Internet from DSL and cable networks. These consumers access theInternet at speeds up to 10-Megabit Ethernet (typical connectivity for a cable-modem service), and for them, a service provider limited to a T1 line is alreadyunacceptably slow.
This requirement to always be faster than your customer (and by afactor of the number of simultaneous accesses) drives the need for T3 (45megabits) or even greater speeds today and will drive the need for Fast Ethernetand Gigabit Ethernet tomorrow. Some carriers are already deploying gigabit optical-Ethernetservices today. They may limit their customers to a few megabits per second, butthe links are gigabit- capable; and someday the fees for gigabit-scale Ethernetservices will be affordable. Then, even a 10-Gigabit–Ethernet transport will beinadequate. Engineers are already dreaming of the next step, and arguing overwhat speed it will be. 40-gigabit speeds (SONET OC–768) have already beendemonstrated, so that is a possible Ethernet target. But the Ethernet “purists”insist that the only logical next step is to move the decimal point one more time—to 100 gigabits. In the meantime, the protocols and techniques for bandwidthsharing over parallel links exist, work well, and are used in thousands of sites. It isa simple step to run parallel optical-Ethernet trunks, each on a separatewavelength, all multiplexed over a single fiber pair using DWDM technology. In this way, a point-to-point Ethernet link could have scores of 10-gigabit channels, with an aggregate Ethernet bandwidth of perhaps 400 gigabits,today! Using recently announced DWDM capacity of 160 wavelengths, 1600-gigabit-per-second links could be implemented. So in a sense, Terabit Ethernet isalready available—of course, this kind of network requires very large Ethernetswitches at the ends of that fiber. The limits on optical-Ethernet bandwidth may just be the limits offiber-optic bandwidth— perhaps 25 Terabits per second for the availablespectrum on today’s fiber, which is still well beyond the capabilities of today’slasers and electronics. Still, extrapolating from recent trends gets us to that levelin only 5 or 10 years.
The advantages of optical Ethernet: · Ethernet is 10 times less expensive than the SONET technology being used today. · Ethernet is a simple and widely understood technology. · Ethernet is the best technology for carrying IP traffic - Ethernet and IP have grown up together. · Optical Ethernet networks can easily handle the needs of both data and circuit- switched or voice applications. Circuit traffic requires only modest bandwidth, REFERENCE 1. www.iec.org 2. www.optical-ethernet.com 3. www.lightreading.com4. Computer Networks - Tannenbaum A 5. www.networkworld.com